The following background description represents a description of the background to the present invention and therefore need not necessarily represent prior art.
The cost of fuel for motor vehicles, e.g. cars, trucks and buses, represents a significant expense for their owner or user. In the case for example of a haulage company, apart from the procurement cost of a vehicle, the main expense items for its routine operation are pay for the driver, repair and maintenance costs and the cost of fuel for the vehicle's propulsion. The fuel cost may here very greatly affect the company's profitability. A wide variety of different systems have therefore been developed for reducing fuel consumption, e.g. fuel-efficient engines and fuel-economising cruise controls.
FIG. 1 depicts schematically a power train of a vehicle 100. The power train comprises a combustion engine 101 which in a conventional way is connected, via an output shaft 102 from the engine, usually via a flywheel, to an input shaft 109 of a gearbox 103 via a clutch 106. The clutch may for example take the form of an automatically operated clutch and may be operated by the vehicle's control system via a control unit 900 (FIG. 9), which may also operate the gearbox 103.
The gearbox 103 is here illustrated schematically as a unit but might physically also take the form of a plurality of interacting gearboxes, e.g. a range gearbox, a main gearbox and a split gearbox, which are situated along the vehicle's power train. The gearbox may comprise a suitable number of gear positions. Today's gearboxes for heavy vehicles usually have twelve gears for travelling forwards, two reverse gears and a neutral gear position. If the gearbox 130 physically comprises two or more divisional gearboxes as above, these twelve forward gears are divided into two in the range gearbox, three in the main gearbox and two in the split gearbox, making a total of twelve gear positions (2*3*2=12). The vehicle 100 further comprises driveshafts 104, 105 which are connected to its tractive wheels 110, 111 and are driven by an output shaft 107 from the gearbox 103 via an axle gear 108, e.g. a conventional differential.
The vehicle 100 further comprises various different brake systems, e.g. a conventional service brake system which may for example comprise brake discs with associated brake linings (not depicted) adjacent to each wheel. The engine 101 may be controlled on the basis of instructions from a cruise control in order to maintain a constant actual vehicle speed and/or to vary the actual vehicle speed so as to achieve optimized fuel consumption within reasonable speed limits. The engine 101 may also be controlled by a driver of the vehicle.